The field of the present invention is control of air driven diaphragm pumps.
Pumps having double diaphragms driven by compressed air directed through an actuator valve are well known. Reference is made to U.S. Pat. No. 5,169,296; U.S. Pat. No. 4,247,264; U.S. Pat. No. Design 294,946; U.S. Pat. No. Design 294,947; and U.S. Pat. No. Design 275,858, all issued to James K. Wilden, the disclosures of which are incorporated herein by reference. An actuator valve operated on a feedback control system is disclosed in U.S. Pat. No. 3,071,118 issued to James K. Wilden, the disclosure of which is also incorporated herein by reference. This feedback control system has been employed with the double diaphragm pumps illustrated in the other patents.
Such pumps include an air chamber housing having a center section and two concave discs facing outwardly from the center section. Opposing the two concave discs are pump chamber housings. The pump chamber housings are coupled with an inlet manifold and an outlet manifold through ball check valves positioned in the inlet passageways and outlet passageways from and to the inlet and outlet manifolds, respectively. Diaphragms extend outwardly to mating surfaces between the concave discs and the pump chamber housings. The diaphragms with the concave discs and with the pump chamber housings each define an air chamber and a pump chamber to either side thereof. At the centers thereof, the diaphragms are fixed to a control shaft which slidably extends through the air chamber housing.
Actuator valves associated with such pumps have included feedback control mechanisms including a valve piston and airways on the control shaft attached to the diaphragms. Air pressure is alternately generated in each air chamber according to control shaft location, driving the diaphragms back and forth. In turn, the pump chambers alternately expand and contract to pump material therethrough. Such pumps are capable of pumping a wide variety of materials of widely varying consistency.
FIG. 1 illustrates a previously designed bushing PA1 to receive a shaft with axial slots cut into the surface which moves axially through the central control passageway of the bushing. The bushing PA1 has four annular channels PA2, PA3, PA4 and PA5 to either side of the center. From the center toward the ends of the bushing, the second and fourth channels
and PA5 of each set of four receive O-rings PA6 to act as annular seals between the bushing PA1 and the shaft in order that flow may be controlled between the central annular channels PA4 and vent channels PA2. The valving mechanism provided by the shaft and the bushing PA1 cooperates with a control valve to alternately vent either end of a shuttle piston at the ends of the stroke of the shaft through the channels PA4. The venting occurs when the axial slots of the shaft span alternately the two channels PA3 containing O-rings PA6 to expose the central annular channels PA4 to the vent channels PA2. This arrangement has long been employed because of the need to rapidly vent the appropriate passage of the control valve.
FIG. 2 also illustrates a previously designed bushing PA7. The bushing PA7 uses the same shaft as the bushing PA1 of FIG. 1 with the axial slots. The bushing PA7 has the same set of annular channels PA2, PA3, PA4 and PA5. The second and fourth channels PA3 and PA5 again contain O-rings PA6 for sealing against the shaft. In addition, slipper seals PA8 of PTFE are positioned in the channels PA3 and PAS. These seals PA8 were independent of the O-rings PA6 and could glide between edges of the channels PA3 and PAS. The bushing PA7 is of plastic and has no relief between the second and third channels PA3 and PA4 which would otherwise be provided through an increased diameter of the passageway through the bushing at that wall. Such a relief is illustrated in the bushing PA1 of FIG. 1 which is a brass design incapable of using the slipper seals PA8. Such a relief would allow the slipper seals PA8 to slide from the channel PA3 in the brass bushing PA1. The design of FIG. 2 is used as a lubrication free design compromising performance by eliminating the relief and reducing the air flow in exchange for the advantages provided by the slipper seals PA8.